Electromagnetic interference (EMI) is a common problem in operating of electronic equipment. EMI is unwanted electromagnetic energy entering or emitting from a designated piece of equipment, thereby causing interference. EMI can cause electronic equipment to function improperly or to not function at all.
Typically, electronic equipment is housed within metallic cabinets which help reduce the EMI problems. These cabinets or structures generally have openings, such as doors or panels which are removable so that the electronic equipment may be serviced or replaced. Some gaps, openings or discontinuities between the cabinet frame and a door or panel allow the EMI to pass into or out of the cabinet, which can cause the failure of the electronic equipment in and around the cabinet.
One of the most widely used EMI shielding devices is a metal strip, commonly referred to as a finger stock. A finger stock is generally formed of beryllium copper or phosphor bronze and is shaped into a "V" or "U" having a number of resilient elements or "fingers" extending out from the center of the material and at least one of the arms. A finger stock is typically difficult to install (i.e., labor intensive) and requires a sufficient force be applied to it in order to achieve electrical continuity between the door or panel and the cabinet. Additionally, the finger stock is made of metal and is, thus, susceptible to fatigue. Repeated physical manipulation of a finger stock can cause the fingers to break off or be permanently compressed. In the case of either event, the shielding properties of the finger stock are substantially degraded or destroyed. A metal finger stock, therefore, requires routine and regular maintenance to oversee its condition, ultimately increasing its cost.
Alternatively, gaskets have been used to produce an electrically conductive contact. Particularly effective types of gaskets are known as spring finger strips. These spring fingers have a range of flexibility which permits them to adapt to unevenness mating surfaces. However, finger strips are limited by their compression range, which limits their maximum compression in order to prevent permanent deformation, or complete rupture, of the gasket. Thus, finger strips are not completely satisfactory. An additional disadvantage of known spring finger gaskets is if they are prone to damage due to snagging. Therefore, these materials have a very low elastic limit and can be permanently deformed under load.
One prior art EMI clip which avoids the snagging of the fingers or ends of the clip is shown in FIGS. 1A and 1B. Referring to FIGS. 1A and 1B, the top view and side view of the prior art clip are shown, respectively, with reference to a metal cabinet or structure to which it is attached. Referring to FIG. 1A, the top view of the prior art clip 10 is shown coupled to the mating surface 11 through slots 12 and 13. Clip 10 consists of a single sheet of conductive material. Each end of clip 10 is placed into a separate slot. Both ends of clip 10 are folded under the body of clip 10, such that the ends anchor clip 10 behind the wall of mating surface 11. Clip 10 has a slot 14. Slot 14 allows the clip to connect to uneven mating surfaces because the part of clip 10 on each side of slot 14 acts somewhat as a spring. Thus, slot 14 provides clip 10 with a dual spring nature, wherein one of the sides on each side of the slot can independently make contact to another mating surface.
FIG. 1B shows the side view of clip 10 in relation to the mating surface 11 and slots 12 and 13. Clip 10 is shown having three arcs A, B and C. Two of the arcs A and B bend the ends of the clip towards themselves. The end of clip 10 coupled to arc A is longer than the end of clip 10 coupled to arc B. Thus, FIGS. 1A and 1B show prior art clip 10 having protected ends to combat snagging. The other arc C in prior art clip 10 causes clip 10 to form a half elliptical side on its top portion, such that when the inner surface of the clip is resting on the flat surface at mating surface 11, the inner surface of clip 10 only makes contact with two parts of the flat mating surface. Thus, the remaining portion of clip 10 directly above the surface is arced away from the mating surface.
One of the problems with the prior art clip 10 of FIGS. 1A and 1B is the difficulty of its installation. Clip 10 is typically installed in a cabinet or card case having two parallel slots. The top view of such a cabinet is shown in FIG. 2A. It should be noted that one of the slots may be smaller than the other. The procedure for installing the prior art clip 10 is shown in FIGS. 2B-D. The first step of installing the clip is shown in FIG. 2B. Initially, the big end of clip 10 (i.e., the end having arc A) must be inserted into the small slot 12 in a downward motion as indicated by the arrow. Then, as shown in FIG. 2C, clip 10 must be pushed toward the edge of the flange (i.e., the direction of the arrow) until the other end of clip 10 snaps in. FIG. 2D shows how the clip should look once installation has been completed. It should be noted that the installation requires two separate steps, each requiring a movement in two distinct directions. Because this multi-directional installation of prior art clip 10 is so labor-intensive, it can be very costly and time consuming for a high volume process.
As will be shown, the EMI clip of the present invention allows a wide variation of gaps between adjacent sheet metal substrates. The EMI clip of the present invention holds up over repeated insertions and extractions by allowing for backward and forward sliding motion of an adjacent sheet metal substrate. The present invention also provides added durability by protecting the flexible exposed ends behind the supporting substrate panel (i.e., mating surface). Furthermore, the present invention includes a center slot and dual springs (or multiple slots and springs) to allow for successful grounding between uneven meeting surfaces. Moreover, the present invention provides a clip which is automatically insertable using a motion directed in a single direction.